The present invention relates to a sound image localization apparatus which realizes rear virtual sound image localization by outputting, from front speakers, rear channel sounds that have been subjected to signal processing that uses head-related transfer functions which simulate spatial propagation characteristics from the surroundings to human ears.
Recently, various apparatus have been disclosed which realize various kinds of sound image localization by using model head-related transfer functions (hereinafter abbreviated as “head-related transfer functions) which simulate spatial propagation characteristics from the surroundings to human ears. Furthermore, since arranging real multi-channel speakers results in a large-scale system and is not practical, a sound image localization apparatus has been proposed which realizes rear virtual sound image localization by performing crosstalk cancellation which cancels spatial propagation characteristics and adds rear sound image localization (JP-A-2001-86599). The crosstalk cancellation is considered a prerequisite for the addition of rear localization. That is, to realize accurate sound image localization, it is considered necessary to add rear sound image localization on condition that spatial propagation characteristics are canceled.
In the crosstalk cancellation, signal processing is performed to produce an effect that a sound generated by a front-left speaker is solely input to the left ear and a sound generated by a front-right speaker is solely input to the right ear by performing inverse transform on head-related transfer functions that simulate propagation characteristics from the front speakers. The crosstalk cancellation thereby produces an effect that a listener feels as if he or she were using a headphone.
In JP-A-2001-86599, FIG. 19 shows a crosstalk canceling method.
However, the crosstalk cancellation has a problem that it generally requires inverse transform calculations and hence requires large-scale processing. Furthermore, the manner of spatial propagation of a sound to an ear depends on each person because a sound is diffracted differently depending on the face width etc. Because of such a difference among individuals, there may occur a case that the effect of the rear virtual sound image localization (i.e., a listener feels as if he or she were hearing a sound coming from behind) is not obtained at all. Another problem of this sound image localization is that it is effective in a pinpointed manner, that is, it is sensitive to the installation angles of speakers and the face direction.